Message-ID: <20231027183636.GA11382@frogsfrogsfrogs>
Date:   Fri, 27 Oct 2023 11:36:36 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Mateusz Guzik <mjguzik@...il.com>
Cc:     Dave Chinner <david@...morbit.com>,
        Christian Brauner <brauner@...nel.org>,
        Dave Chinner <dchinner@...hat.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-bcachefs@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: (subset) [PATCH 22/32] vfs: inode cache conversion to hash-bl

On Fri, Oct 27, 2023 at 07:13:11PM +0200, Mateusz Guzik wrote:
> On 10/23/23, Dave Chinner <david@...morbit.com> wrote:
> > On Fri, Oct 20, 2023 at 07:49:18PM +0200, Mateusz Guzik wrote:
> >> On 10/20/23, Dave Chinner <david@...morbit.com> wrote:
> >> > On Thu, Oct 19, 2023 at 05:59:58PM +0200, Mateusz Guzik wrote:
> >> >> > To be clear there is no urgency as far as I'm concerned, but I did
> >> >> > run
> >> >> > into something which is primarily bottlenecked by inode hash lock
> >> >> > and
> >> >> > looks like the above should sort it out.
> >> >> >
> >> >> > Looks like the patch was simply forgotten.
> >> >> >
> >> >> > tl;dr can this land in -next please
> >> >>
> >> >> In case you can't be arsed, here is something funny which may convince
> >> >> you to expedite. ;)
> >> >>
> >> >> I did some benching by running 20 processes in parallel, each doing
> >> >> stat
> >> >> on a tree of 1 million files (one tree per proc, 1000 dirs x 1000
> >> >> files,
> >> >> so 20 mln inodes in total).  Box had 24 cores and 24G RAM.
> >> >>
> >> >> Best times:
> >> >> Linux:          7.60s user 1306.90s system 1863% cpu 1:10.55 total
> >> >> FreeBSD:        3.49s user 345.12s system 1983% cpu 17.573 total
> >> >> OpenBSD:        5.01s user 6463.66s system 2000% cpu 5:23.42 total
> >> >> DragonflyBSD:   11.73s user 1316.76s system 1023% cpu 2:09.78 total
> >> >> OmniosCE:       9.17s user 516.53s system 1550% cpu 33.905 total
> >> >>
> >> >> NetBSD failed to complete the run, OOM-killing workers:
> >> >> http://mail-index.netbsd.org/tech-kern/2023/10/19/msg029242.html
> >> >> OpenBSD is shafted by a big kernel lock, so no surprise it takes a
> >> >> long
> >> >> time.
> >> >>
> >> >> So what I find funny is that Linux needed more time than OmniosCE (an
> >> >> Illumos variant, fork of Solaris).
> >> >>
> >> >> It also needed more time than FreeBSD, which is not necessarily funny
> >> >> but not that great either.
> >> >>
> >> >> All systems were mostly busy contending on locks and in particular
> >> >> Linux
> >> >> was almost exclusively busy waiting on inode hash lock.
> >> >
> >> > Did you bother to test the patch, or are you just complaining
> >> > that nobody has already done the work for you?
> >>
> >> Why are you giving me attitude?
> >
> > Look in the mirror, mate.
> >
> > Starting off with a derogatory statement like:
> >
> > "In case you can't be arsed, ..."
> >
> > is a really good way to start a fight.
> >
> > I don't think anyone working on this stuff couldn't be bothered to
> > get their lazy arses off their couches to get it merged. Though you
> > may not have intended it that way, that's exactly what "can't be
> > arsed" means.
> >
> > I have not asked for this code to be merged because I'm not ready to
> > ask for it to be merged. I'm trying to be careful and cautious about
> > changing core kernel code that every linux installation out there
> > uses because I care about this code being robust and stable. That's
> > the exact opposite of "can't be arsed"....
> >
> > Further, you have asked for code that is not ready to be merged to
> > be merged without reviewing it or even testing it to see if it
> > solved your reported problem. This is pretty basic stuff - it you
> > want it merged, then *you also need to put effort into getting it
> > merged* regardless of who wrote the code. TANSTAAFL.
> >
> > But you've done neither - you've just made demands and thrown
> > hypocritical shade implying busy people working on complex code are
> > lazy arses.
> >
> 
> So I took few days to take a look at this with a fresh eye and I see
> where the major disconnect is coming from, albeit still don't see how
> it came to be nor why it persists.
> 
> To my understanding your understanding is that I demand you carry the
> hash bl patch over the finish line and I'm rude about it as well.
> 
> That is not my position here though.
> 
> For starters my opening e-mail was to Christian, not you. You are
> CC'ed as the patch author. It is responding to an e-mail which claimed
> the patch would land in -next, which to my poking around did not
> happen (and I checked it's not in master either). Since there was no
> other traffic about it that I could find, I figured it was probably
> forgotten. You may also notice the e-mail explicitly states:
> 1. I have a case which runs into inode hash being a problem
> 2. *there is no urgency*, I'm just asking what's up with the patch not
> getting anywhere.
> 
> The follow up including a statement about "being arsed" once more was
> to Christian, not you and was rather "tongue in cheek".

I thought that was a very rude way to address Christian.

Notice how he hasn't even given you a response?

"Hello, this patch improves performance for me on _______ workload.
What needs to be done to get this ready for merging?  I'd like to
take on that work."

--D

> If you know about Illumos, it is mostly slow and any serious
> performance work stopped there when Oracle closed the codebase over a
> decade ago. Or to put it differently, one has to be doing something
> really bad to not be faster today. And there was this bad -- the inode
> hash. I found it amusing and decided to share in addition to asking
> about the patch.
> 
> So no Dave, I'm not claiming the patch is not in because anyone is lazy.
> 
> Whether the patch is ready for reviews and whatnot is your call to
> make as the author.
> 
> To repeat from my previous e-mail I note the lock causes real problems
> in a real-world setting, it's not just microbenchmarks, but I'm in no
> position to test it against the actual workload (only the part I
> carved out into a benchmark, where it does help -- gets rid of the
> nasty back-to-back lock acquire, first to search for the inode and
> then to insert a new one).
> 
> If your assessment is that more testing is needed, that makes sense
> and is again your call to make. I repeat again I can't help with this
> bit though. And if you don't think the effort is justified at the
> moment (or there are other things with higher priority), so be it.
> 
> It may be I'll stick around in general and if so it may be I'm going
> to run into you again.
> With this in mind:
> 
> > Perhaps you should consider your words more carefully in future?
> >
> 
> On that front perhaps you could refrain from assuming someone is
> trying to call you names or whatnot. But more importantly if you
> consider an e-mail to be rude, you can call it out instead of
> escalating or responding in what you consider to be the same tone.
> 
> All that said I'm bailing from this patchset.
> 
> Cheers,
> -- 
> Mateusz Guzik <mjguzik gmail.com>
> 

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